1. Field of the Invention
This invention relates to a recording medium to be used for the system which performs recording, reproduction and erasing of information by use of a probe electrode, and a method for preparing the same.
Also, the present invention relates to a recording and reproducing device and a recording, reproducing and erasing method by use of such recording medium.
2. Related Background Art
In recent years, uses of memory materials form the nucleus of electronics industries such as computers and their related instruments, video discs, digital audio discs, etc. and developments of their materials are also under active progress. The performances demanded for memory materials may differ depending on uses, but may generally include:
(1) high density and large recording capacity; PA1 (2) rapid response speed of recording and reproduction; PA1 (3) excellent stability; PA1 (4) little error rate; PA1 (5) small power consumption; PA1 (6) high productivity and low cost; etc.
Heretofore, semiconductor memories or magnetic memories employing magnetic material or semiconductor as the base material have been predominant, but with the advancement of laser technique, inexpensive and high density recording media with optical memory by use of an organic thin film such as organic dye, photopolymer, etc. are now emerging in the field of art.
However, in the case of an optical memory by use of an organic thin film as the recording layer, in spite of such advantages that the cost is very low because an organic material is employed and also that the density is high because a laser beam is employed for recording and reproduction, particularly light fastness is inferior because a material reactive with light (particularly UV-ray) is employed as the recording layer, whereby a problem has been involved in stability. Also, for improvement of light fastness, there may be employed the method of mixing a UV-absorber with the organic material itself, or covering the recording layer with a UV-absorbing film, but in this case, the reactivity with light becomes contrariwise poor, whereby recording sensitivity is inferior. As the result, should, for example, writing and reproduction be performed with the same recording power as usual, there was involved the problem that the error rate became larger. Thus, in the case of an optical memory which performs recording and reproduction by use of light, in its characteristics, there has been involved the problem that light fastness, namely stability, is poor, or that error rate becomes poor.
As different from optical recording, a recording and reproducing device which performs writing and reading of information by use of a probe electrode onto a recording medium comprising an organic thin film for the recording layer is disclosed in Japanese Patent Laid-Open Nos. 63-161552 and 63-161553.
The recording medium disclosed in such publications, probably because the recording layer is exposed on the surface, is susceptible to deterioration (inferior in environmental resistance) due to action by light or humidity when, for example, an organic material is used as the recording layer, whereby electrical characteristics will also be readily changed.
For cancelling such inconveniences, one may also consider to provide a protective layer on the recording layer surface.
However, to be used for the system which performs reproduction of recording by detection of the current value flowing between the recording medium and the probe electrode, the protective layer is required to be made sufficiently thin, but if the thickness is made thin, there is contrariwise the drawback that the layer will not function as the protective layer.
Also, in the prior art example, it will take a long time for fine control of the distance between the recording medium surface and the probe electrode, and also it is not easy to maintain always the distance constantly, whereby the current-voltage characteristics are liable to become unstable.